Microwave and millimeter wave multichip assemblies are expensive to design and develop and require substantial labor commitments to manufacture. Prototyping and production lead times are long and yield rates are low. Traditional monolithic microwave integrated circuit (MMIC) assemblies are produced with machined metal housings, generally of aluminum or Kovar material and use alumina, beryllia, aluminum nitride or similar co-fired ceramic substrates. These prior art assemblies are multiple material systems fabricated using many different process steps. These process steps are costly since the assemblies cannot be fabricated in a fully automated operation in large quantities by such processing techniques.
In a traditional MMIC assembly, a fired ceramic substrate is provided for structural integrity. Circuits are then built on the substrate in stacked layers. Each layer starts with "green" state materials and is then processed in the "green" state (screen-printing, via formation, etc.). Each layer is then cured at a slightly elevated temperature (&lt;100.degree. C.) so that the metalization is dried and will stick to the "green" ceramic layers for the duration of processing. Several different layers are produced in this manner as required for the final assembly. The built-up layers are then pressed together so that the materials of adjacent "green" layers contact each other. The assembly is then heated to temperatures ranging from 800.degree. to 1800.degree. C. to sinter the ceramic material.
Besides the complex processes required to produce traditional MMIC assemblies, ceramics have inferior mechanical properties. The disadvantages include susceptibility to cracking and lower reliability. Furthermore, ceramic substrates do not allow large numbers of user channels to be formed from a single antenna aperture. This leads to weight and cost penalties at the spacecraft level.
Thus there is a need for a microwave phased array assembly using conventional (PWB) processes, which includes integrated RF, digital, analog and antenna elements, as well as other possible functions, such as I/O.